The invention relates to a camshaft adjusting device including an actuator for adjusting the phase position of a camshaft with respect to a crankshaft of an internal combustion engine while maintaining a basic drive torque.
It is known that, in camshaft adjusting devices composed of a summing gearing and rotary actuator, the camshaft drive torque is backed by at the positioning input. A base torque which is to be present is provided by the actual camshaft torque divided by the transmission ratio of the summing gearing. The positioning actuator which is connected to the positioning input, for example an electric motor or a brake, must constantly apply the torque which is to be backed up by some component. If an auxiliary unit, for example a high-pressure injection pump, is additionally connected to the camshaft so as to be driven thereby, then the torque which is to be backed up also increases at the positioning input, as a result of which the positioning actuator must be larger. Power consumption and, in the case of a passive camshaft adjusting device having a brake, brake losses are correspondingly increased. It is therefore generally preferable for auxiliary units not to be driven by the camshaft.
U.S. Pat. No. 5,234,088 A1 discloses a camshaft adjusting device in which a clutch is connected in series between a drive input shaft and drive output shaft. A constant torque as a result of friction effects is superposed on cyclic torque fluctuations which are generated by the crankshaft operating the engine inlet and outlet valves and which are utilized for phase adjustment of the camshaft by virtue of the latter being correspondingly braked or accelerated. If the camshaft adjusting device is used in a drivetrain in which the torque fluctuations are small enough that a summed torque composed of fluctuations and constant torque is positive overall, it is possible for a spring element which is preloaded in one rotational direction to be arranged parallel to the camshaft adjusting device, so that the spring element completely or partially compensates the constant torque. In this way, the positive and negative components of the torque fluctuations are available entirely to the camshaft adjusting device for accelerating or braking the camshaft. In the case of a low constant torque, when the torque fluctuations result in negative components even in the summed torque, the spring element can be dispensed with. The spring element should, in addition to the torque generated by friction effects, also compensate for torques, which result from the operation of auxiliary units driven by the camshaft other than the valves.
It is the principal object of the present invention to provide a camshaft adjusting device which makes it possible to drive auxiliary units via the camshaft independently of an adjusting direction and without a significant increase in the torque to be backed up by the camshaft adjusting device.